In biology, decomposition occurs when an organisms that is no longer living decays into smaller parts. This process returns nutrients to the environment. Organisms that aid in the process of decomposition are called decomposers. Decomposers include bacteria, fungi, and some worms. Decomposers consume dead or decaying organisms. In this way, decomposers break down the dead or decaying organisms into simpler forms of matter that can be reused within an ecosystem. Thus, decomposers are important parts of food webs.
In chemistry, a decomposition reaction is a chemical reaction in which a single compound breaks apart into two smaller compounds, molecules, or elements. Such reactions are often aided by the input of energy from either heat, light, or electricity. This energy is used to break the bonds of the substance that is undergoing the decomposition reaction.